The present invention relates to a miniature microphone component that is optimized for insertion into the main body of a small-size communication device such as a mobile phone or a mobile radio.
At present, the development of ever smaller and lighter small-size portable communication devices is well-established, and thus microphone elements to be used as components of such communication devices are also becoming smaller. For the installation of a miniature microphone in such a communication device, a thin lead wire is soldered to connect the terminals of the miniature-microphone-side to the terminals on a circuit board in the main body of the small-size communication device, and then the miniature microphone is covered with a rubber casting as a seal against vibrations and inserted into the small-size communication device.
However, the process of attaching the miniature microphone by soldering with a thin lead wire leads to the problems that the product quality is not steady, because this process involves a delicate soldering job that has to be performed by hand and hardly can be automatized, and the installation space cannot be made narrower, since the lead wire has to be connected.
In order to overcome these problems of the prior art, it is a purpose of the present invention to provide a miniature microphone component with conductive rubber contacts for an installation method wherein the soldering job is eliminated, thus facilitating the assembly, and the installation space can be made very small.
In order to achieve the above purpose, a miniature microphone component according to the present invention comprises (electrically) conductive rubber contacts and a rubber casting for protection against vibrations covering the circumference of a miniature microphone. The conductive rubber contacts are formed and fixed on a terminal area of the miniature microphone. The miniature microphone, the rubber casting for protection against vibrations covering the miniature microphone and the conductive rubber contacts are integrated into one component. Due to this configuration, the miniature microphone component according to the present invention can be assembled easily just with pressure contacting it to terminals on a circuit board and the jobs of soldering and connecting a lead wire can be omitted. As a result, the assembly can be facilitated and an installation method for a very small installation space can be used.
It is preferable that the rubber casting for protection against vibrations is made of silicone rubber, because its durability is high and its protection against vibrations is excellent.
From the viewpoint of material mixture, it is preferable that at least one rubber selected from the group consisting of polybutadiene, natural rubber, polyisoprene, SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), EPDM (ethylene-propylene rubber (ternary copolymer)), EPM (ethylene-propylene rubber), polyurethane-polyester-based rubber, chloroprene rubber, epichlorohydrin rubber and silicone rubber is used as a material for the conductive rubber contacts, but considering its electrical properties and weather resistance, silicone rubber is the most preferable. Moreover, to ensure conductivity, it is preferable that the conductive rubber contacts comprise carbon powder. It is preferable that the conductive rubber contacts contains 10-150 weight parts carbon powder per 100 weight parts rubber component, preferably silicone rubber. More preferable are 40-100 weight parts carbon powder. Good conductivity is not attained, when the added amount of carbon powder is below these ranges. When the added amount of carbon powder is above these ranges, the conductivity hardly increases, and the formability and the compression resilience of the conductive rubber contacts are inhibited.
To ensure an even higher conductivity, it is preferable that the conductive rubber contacts comprise at least one powder selected from the group consisting of: a metal powder containing platinum, gold, silver, nickel, cobalt, copper, tin, aluminum or palladium; an alloy powder containing solder; a conductive powder of organic polymer powder that has been coated with a metal; and a conductive powder of inorganic powder that has been coated with a metal. Such a powder can be added in addition to the carbon powder or in place of the carbon powder. It is preferable that the conductive rubber contacts contain 1-400 weight parts powder per 100 weight parts rubber component, preferably silicone rubber. More preferable are 100-300 weight parts. Better conductivity is not attained when the added amount of powder is below these ranges. When the added amount of the powder is above these ranges, the conductivity hardly increases, and the formability and compression resilience of the conductive rubber contacts are inhibited.
The volume resistivity of the conductive rubber contacts should be in the range between 10xe2x88x924 xcexa9 cm and 102 xcexa9 cm. More preferable is a volume resistivity between 10xe2x88x923 xcexa9 cm and 10 xcexa9 Q cm. It is not useful to employ a volume resistivity below these ranges, because then the material costs are high and the rubber resilience is low. If the volume resistivity is above these ranges, the attained conductivity is not suitable and may be unsatisfactory.
It is preferable that the conductive rubber contacts are elastically compressible and can be area-contacted under pressure-induced elastic deformation of the conductive rubber contacts to a terminal portion on a circuit board. With such a configuration, the conductive rubber contacts deform elastically when contacted with the terminals of a circuit board, so that the reliability of the electrical contact is increased. Furthermore, because the miniature microphone is clamped and retained by the conductive rubber contacts and the rubber casting against vibrations, its resistance against vibrations is increased. It is preferable that the conductive rubber contacts have a compression resilience of 30-80 measured with Method A in JIS K6301. If the compression resilience is below this range, the elastic deformation of the conductive rubber contacts becomes large, and the conductivity becomes pressure sensitive, so that the electric contact resistance to the terminals of the circuit board becomes unstable. If the compression resilience is above this range, the elastic deformation of the conductive rubber contacts becomes small, so that the reliability of the electric contact to the terminals of the circuit board decreases. Method A in JIS K6301 for measurement of the compression resilience is performed as follows: A sample piece of the size specified in JIS K6301 is prepared from the material to be tested. An A-type spring-based hardness meter according to JIS K6301 is used as measuring instrument. Method A in JIS K6301 is in conformity with Type A in ASTM D2240.
In the above miniature microphone component with conductive rubber contacts, a highly reliable electrical planar contact can be established just by slightly compressing the conductive rubber contacts, which are formed and fixed to the terminal area of the miniature microphone, between the terminal areas on the circuit board inside the small-size communication device and the terminal area of the miniature microphone. Soldering of a lead wire to establish contact with a circuit board becomes obsolete. Thus, not only can the installation space be made much smaller, but a troublesome installation job can be eliminated.
In addition, the rubber casting (also called xe2x80x9cbushingxe2x80x9d in the following) for protection against vibrations is shaped so that it can hermetically cover the miniature microphone completely, except for the terminal area and a sound-collecting portion. This rubber casting can be integrated with the miniature microphone and the conductive rubber contacts, so that the miniature microphone component with conductive rubber contacts can be installed just by inserting it into a predetermined location inside a small-size communication device, which considerably increases the working efficiency of the assembly.
The use of the rubber casting (bushing) as a protection against vibrations of course enhances the reliability of the miniature microphone under vibrations, and when the miniature microphone component is built into a small-size communication device, the pressure between the conductive rubber contacts formed and fixed on the microphone terminal area and the circuit board terminal area is held constant due to the rubber resilience of the bushing. Thus, the additional effect of an electric contact with high reliability is achieved.
The miniature microphone component according to the present invention can be used for all kinds of applications, but it is preferable that it is used to be inserted into a miniature portable communication device such as a mobile phone. The miniature microphone component according to the present invention can be assembled without soldering a lead wire to it, so that the installation space can be minimized. Electrical reliability and vibration resistance can be increased simultaneously, because the miniature microphone is clamped in and retained by the conductive rubber contacts and the rubber casting against vibrations. This can add to the product value of small-size portable communication devices, for which an increase of miniaturization and reliability is especially desirable.
As has been pointed out above, in a miniature microphone component with conductive rubber contacts according to the present invention, a highly reliable electrical contact can be established just by slightly compressing the conductive rubber contacts, which are formed and fixed to the miniature microphone terminal area, between the terminal areas on the circuit board inside the small-size communication device and the terminal area of the miniature microphone. Soldering of a lead wire to establish contact with a circuit board becomes obsolete. Thus, not only can the installation space be made much smaller, but a troublesome installation job can be eliminated.
In addition, the rubber casting (bushing) for protection against vibrations is shaped so that it can hermetically cover the entire miniature microphone except for the terminal area and a sound-collecting portion. This rubber casting can be integrated with the miniature microphone and the conductive rubber contacts, so that the miniature microphone component with conductive rubber contacts can be installed just by inserting it into a predetermined location inside the small-size communication device, which considerably increases the working efficiency of the assembly. The use of the bushing as a protection against vibrations enhances of course the reliability of the miniature microphone under vibrations, and when the miniature microphone component is built into a small-size communication device, the pressure between the microphone terminal area and the circuit board terminal area is held constant due to the rubber resilience of the bushing. Thus, the additional effect of an electric contact with high reliability is achieved.